This invention relates to an oleo-pneumatic shock absorbing system. More particularly, the invention provides a shock absorber wherein the oil and the gas, instead of being contained in a single cylinder, are distributed inside cells, and wherein particularly, oil is contained in a cell in the form of bellows whose internal volume changes in response to external force.
An oleo-pneumatic shock absorber is a device which decelerates a moving mass and converts much of its kinetic energy into heat due to the friction of oil being driven through narrow orifices. Although a conventional spring can also be arranged to decelerate a moving mass, the converted kinetic energy is stored as elastic deformation energy and not dissipated. A further significant difference between these two devices is that the spring provides increasingly higher resistance over its stroke, whereas an oleo-pneumatic shock absorber is designed to provide rapidly increasing resistance to a certain maximum, whereafter the resistance remains essentially constant. The consequence of this difference is that, for an equal maximum resistance, the oleo-pneumatic decelerate an equal moving mass over a much shorter distance.
Oleo-pneumatics have been known for many decades and are commonly used on medium size and large aircraft. Such devices contain oil which is driven through narrow orifices in a piston moving inside a cylinder and high pressure nitrogen that is further rapidly compressed during the beginning of the energy absorbing stroke.
Some shock absorbers use a compressed gas as the fluid absorbing energy and converting it into heat.
An example of a shock absorber using only a compressed gas is described by Higginbotham in U.S. Pat. No. 3,692,296.
A complex absorber using both oil and compressed gas is disclosed by Allinquant et al. in U.S. Pat. No. 3,837,444.
Prior art shock absorbers have a moving piston rod which requires a seal, which is subject to wear and deterioration. Also required are sealing end covers.
Prior art shock absorbers have certain disadvantages. In prior art oleo-pneumatic shock absorbers the piston rod can rotate relative to the cylinder cover through which it protrudes. Where such rotation is not desired a device must be provided to prevent this.
There is a need to accede into the oil cell for topping up with hydraulic oil to replace that which is lost by leakage. Alternatively, the whole shock absorber needs to be replaced after losing oil during service.
Primarily the above factors are responsible for the limited life of prior art absorbers, although there are additional problems resulting from metal fatigue.
It is therefore one of the objects of the present invention to obviate most of the disadvantages of prior art shock absorbers and to provide a device which greatly reduces the need for maintenance.
It is a further object of the present invention to provide a light weight shock absorber advantageous for use on vehicles and aircraft.
The present invention achieves the above objects by providing a shock-absorbing system, comprising a n oil cell having bellows-shaped sidewalls and a bi-fluid cell, said cells being in fluid communication with each other via at least one flow restriction conduit.
In the present specification:
A bi-fluid cell is defined as a vessel containing a constant quantity (by mass) of gas and a variable quantity of oil during operation.
A flow restriction conduit is a narrow aperture, orifice, tube, hose or pipe through which oil flows between the oil cell and the bi-fluid cell during operation.